LRS30,
The pipe 1/2" pvc and is 2 ft long. I created the flaps after cutting away unwanted plastic.
I then took the plastic and held it above the stove's gas flame until it softens, about 30 seconds and then bent it with pliers.
Once the basic bend is done it can be further shaped with your fingers and held until it hardens. This process can be repeated until you get it right.
A heat gun, torch, maybe even a hair dryer may be used. Keep it high enough so it doesn't burn.
For me it was a trial and error process.
I used black tywraps to hold the top of the rock guard but I think Carol's approach of using small hose clamps is better. Tywraps eventually UV fail.